Again a cross post from another thread, as this again regards PS3 technicals I think this is very suited for this thread. This time with regard to claims of the SPEs being useless with regard to pixel shading:
Some initial research indicating the contrary:
"This paper studies a deferred pixel shading algorithm implemented on a Cell-based computer entertainment system. The pixel shader runs on the Synergistic Processing Units (SPUs) of the Cell and works concurrently with the GPU to render images. The system's unified memory architecture allows the Cell and GPU to exchange data through shared textures. The SPUs use the Cell DMA list capability to gather irregular fine-grained fragments of texture data generated by the GPU. They return resultant shadow textures the same way. The shading computation ran at up to 85 Hz at HDTV 720p resolution on 5 SPUs and generated 30.72 gigaops of performance. This is comparable to the performance of the algorithm running on a state of the art high end GPU. These results indicate that a hybrid solution in which the Cell and GPU work together can produce higher performance than either device working alone."
"We have explored moving pixel shaders from the GPU to
the Cell/B.E. processor of the PLAYSTATION®3
computer entertainment system. Our initial results are
encouraging as they show it is feasible to attain scalable
speedup and high performance even for shaders with
irregular fine-grained data access patterns. Removing the
computation from the GPU effectively increases the frame
rate, or more likely, the geometric complexity of the models
that can be rendered in real time.
We can also conclude that the performance of the Cell/B.E.
is superior to a current state of the art high end GPU in that
we achieved comparable performance despite performance
limitations and despite using only part of the available
processing power. Our current implementation loses
substantial performance due to DMA waiting. This results
from the fine-grained irregular access to memory and is
specific to the type of shaders we have chosen to
implement. We have explored shaders based on shadow
mapping [15] which require evaluating GPU fragments
generated from multiple viewpoints. These multiple
viewpoints are related to each other by a linear viewing
transformation. Gathering the data from these multiple
viewpoints requires fine-grained irregular memory access.
This represents worst-case behavior for any memory
system. "
http://research.scea.com/ps3_deferred_shading.pdf
The Cell's SPEs are very flexible with regard to which kinds of code they can help facilitate, the SPEs act as true processors allowing multi-threading and such like I pointed out earlier and are very suited to take workload off the GPU as well as the PPE. This though does mean legacy game engines need to be modified and game development approaches require different programming tactics.
So unless you read articles from Cell programming or hardware design experts IMO take any comments you may read with a grain of salt, seemingly especially if they originate from XBox 360 fans.
